Selvyn Davids had already grounded the ball for South Africa's final try in their 26-12 Pool C win, when Isaac Kaay shoved him in the chest - a clear sign of frustration for Canada, the defending HSBC Singapore Sevens champions.
Kaay got a yellow card for his petulance and the self-destruction of the Canadians was completed later in the evening. They fell 19-22 to Samoa, despite leading twice, to end the defence of the title they won in sensational fashion at the National Stadium last year.
Canada coach Damian McGrath said: "Sometimes teams are too good for you, and you've got to hold your hands up. But we lost twice to teams where we opened the door, let them through. It's our own fault.
"We got well in front, then handed the ball over twice inside our own 22. Good teams don't do that. To hand over your title, you want to do it in the right way, we gave it away really.
"It's very frustrating."
For periods yesterday, it looked like Singapore would live up to its billing as the "surprise sevens" leg of the World Series that has seen two first-time winners on the series: Kenya in 2016 followed by Canada's shock victory.
New Zealand, who won the Commonwealth Games gold this month and have never missed out on a Cup quarter-final appearance in the World Series, had lost 12-19 to Australia in Pool D and were in danger of ending that proud run before edging past Scotland 22-12 to secure their place in the last eight.
SINGAPORE SEVENS DAY 2
1.58pm: Under-14 Singapore schools sevens series final - Anglo-Chinese School (Independent) v St Andrew's Secondary School
12.30pm: Cup quarter-finals
4.50pm: Cup semi-finals
5.24pm: Liver performance by Village People
7.35pm: Bronze match
8pm: Cup final
Fiji v New Zealand
South Africa v Kenya
Australia v Spain
England v Samoa
Kiwi coach Clark Laidlaw put his team's unconvincing display down to inconsistency, this after making five changes to the 13-man squad that triumphed on the Gold Coast two weeks ago.
But it will only get harder as the All Black Sevens face Pool A winners Fiji in today's first quarter-final. It is a repeat of the Commonwealth Games gold medal match.
Laidlaw said: "It's a new group (of players), new combinations, and we're a little bit rusty, but there's excitement for tomorrow. If we can bring the same effort, then who knows what can happen.
"You've seen some really tight pools today, so you've got to beat everybody. We'll take it on the chin and get ready for Fiji."
Australia, under new coach Tim Walsh, and England ended the day with a perfect record of three wins in their respective pools, but that meant little to Walsh.
He said: "Reality is anyone can win anything if you're not prepared properly, so we're going to make sure we're on again tomorrow. It's about waking up tomorrow and in the best physical and mental state."
"I can't complain about today, we got three out of three - that's pretty good. But it's a two-day tournament, you can ask me again tomorrow after (the quarter-final)."
Q-finals (10.45am), s-finals (2.30pm), Finals (6pm) - StarHub Ch112/205 & 76.25MHz.